Thin film photovoltaic (PV) modules (also referred to as “solar panels”) based on cadmium telluride (CdTe) paired with cadmium sulfide (CdS) as the photo-reactive components are gaining wide acceptance and interest in the industry. CdTe is a semiconductor material having characteristics particularly suited for conversion of solar energy to electricity. For example, CdTe has an energy bandgap of about 1.45 eV, which enables it to convert more energy from the solar spectrum as compared to lower bandgap semiconductor materials historically used in solar cell applications (e.g., about 1.1 eV for silicon). Also, CdTe converts radiation energy in lower or diffuse light conditions as compared to the lower bandgap materials and, thus, has a longer effective conversion time over the course of a day or in cloudy conditions as compared to other conventional materials. The junction of the n-type layer and the p-type layer is generally responsible for the generation of electric potential and electric current when the CdTe PV module is exposed to light energy, such as sunlight. Specifically, the cadmium telluride (CdTe) layer and the cadmium sulfide (CdS) form a p-n heterojunction, where the CdTe layer acts as a p-type layer (i.e., a positive, electron accepting layer) and the CdS layer acts as a n-type layer (i.e., a negative, electron donating layer).
A transparent conductive oxide (“TCO”) layer is commonly used between the window glass and the junction forming layers. This TCO layer provides the front electrical contact on one side of the device and is used to collect and carry the electrical charge produced by the cell. While the TCO layer is typically produced from relatively low resistivity materials (e.g., cadmium stannate), the TCO layer still provides resistance to the series of cells in the device. This resistance in the TCO layer can inhibit the flow of electrons through the device, effectively hindering the efficiency of the photovoltaic device, especially cadmium telluride based photovoltaic devices. Increasing the thickness of the TCO layer can reduce the resistance of the front contact, but can also lead to increased material costs and a rough surface morphology that can adversely affect subsequently deposited layers of the device.
As such, a need exists to reduce the series resistance of the front electrical contact (e.g., the TCO layer) in photovoltaic devices, particularly cadmium telluride based photovoltaic devices, with minimal loss of current and without increasing the thickness of the TCO layer.